The foraminifera of the Chalk Group in the North Sea Basin were outlined by Wilkinson et al. (1993, 1994). The biomarkers were selected for borehole samples collected by open-hole methods and those chosen were well known, easily identified and based on those commonly used by industry. Definitions were based on the first down-hole occurrences (i.e. extinctions) and a pragmatic approach was taken; a refined or detailed biostratigraphical subdivision of the Chalk Group was not attempted. As the biomarkers offshore were based on 'tops', they do not fit exactly with the onshore biozonation outlined by Wilkinson (2000), which was based on inceptions, extinction and acmes (biomarkers or bioevents within the zones were also recognised). Nevertheless, the biomarkers of the North Sea succession can be related to the onshore biozones, and the purpose of this report is to relate the two schemes.

The biomarkers identified for offshore sequences were, by necessity, defined from the top down. Each biomarker represents a single event and no attempt was made to place them into a zonal scheme. The biomarkers of the Chalk Group in the North Sea Basin are placed, herein, within the context of the biozones recognised in southern and eastern England.

Descriptions of offshore foraminiferal biomarkers in the Chalk Group

The foraminifera biomarkers recognised in the Upper Cretaceous Shetland Group are not included in this synthesis. Being based on First Downhole Occurrences (FDOs), the highest possible stratigraphical positions for the Biomarkers are given here. However, in some cases, similar faunas may be found lower compared to the foraminiferal zones. Distributions are related to the species ranges of southern and eastern England.

In the following account Biomarkers in the offshore UK Chalk Group are systematically described from youngest (Biomarker 1) to oldest (Biomarker 15). Alternatively, for information about a particulat Biomarker, select it from the summary table (summary correlation of offshore foraminiferal biomarkers and BGS foraminiferal zones).

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